There is a problem here i'm afraid. I can't upload vids with the proxy i use and most upload sites are filtered by gov.
However i can tell you what exactly happens. I write a quick reply ( or quote someone ) when i hit "Post quick reply" or "Submit reply", after 2 seconds when used to take to submit a reply, this error comes from nowhere.
In past i had to refresh page and submit it again, now if i wait for 5 seconds after the error got shown, the reply gets submitted by itself. The error itself doesn't disappear, but if i press "okay" it disappears.